The fermentation industry consumes very large quantities of feedstock materials each year. Successful commercial fermentation depends on designing fermentation media containing nutrient sources optimal for microbial growth and product formation. Bioprocess nutrients include sources of carbon, nitrogen, inorganic components, and vitamins. Often complex xe2x80x9cnaturalxe2x80x9d sources of nitrogen are chosen which supply not only nitrogen, but also carbohydrate, vitamins, minerals, and other microbial growth factors. Commonly used materials include soybean meal or flour, fish meal, and corn steep liquor. All of these crude naturally derived products have the advantage of being relatively inexpensive compared to complex specialty medium ingredients, such as yeast extracts or highly processed oilseed meals.
Since the crude naturally derived products were not designed for fermentation applications, potential drawbacks to their effectiveness exist. For example, these crude materials contain very little readily-available nitrogen. This limits their use as nitrogen sources in fermentation by microorganisms which do not excrete extracellular proteases, and by microbes that require some readily-available nitrogen for growth in the early stages of fermentation prior to effectively utilizing protein. A common measure of the readily available nitrogen in a nutrient is the amount of free amino nitrogen (xe2x80x9cFAN contentxe2x80x9d) of the material. Crude naturally derived materials can also contain significant amounts of insoluble, unusable materials which must be separated from the product of interest and disposed of after fermentation. Finally, since these crude feedstock materials are products of the agricultural and food processing industries, their consistency and/or quality can be variable.
To be an effective nitrogen source in fermentation, protein must generally first be hydrolyzed to its constituent small peptides and individual amino acids. This can be accomplished either during fermentation by proteolytic enzymes excreted by the fermenting microorganism, or provided directly in a pre-digested form as a fermentation medium ingredient. Protein nitrogen in this more bioavailable form is known as free amino nitrogen (xe2x80x9cFANxe2x80x9d). FAN is a measure of the quantity of amino nitrogen available during fermentation, and refers specifically to the amount of small peptides, amino acids, and ammonia Commercial products employed to provide higher FAN in fermentation media include yeast extracts and protein hydrolysates. Potential substrates for hydrolysis include casein or sunflower, rapeseed, soy, meat, and bone meals, and the starting material for the hydrolysis ultimately dictates the composition of the final product.
To supply nitrogen needs in fermentation media, soybean meal and flours are often used in combination with more expensive yeast extracts or soy isolates/concentrates. This combination provides both xe2x80x9creadily-availablexe2x80x9d nitrogen and xe2x80x9cslow-releasexe2x80x9d protein for the duration of the fermentation. The need to supplement crude protein feedstocks with more expensive defined nutrient sources, however, can greatly increase raw material costs.
The latent nutritional values present in many vegetables, particularly the oilseed vegetables such as soybeans and other legumes and cottonseeds, is well known. Utilization of these nutrient sources has been severely hampered, however, by the presence in these vegetable nutrients of naturally occurring substances that can interfere with the growth of organisms. The principal deficiencies of vegetable nutrient sources for use in fermentation media (in addition to low FAN content) are the presence of antinutritional factors such as trypsin inhibitor, lectins and phytic acid. While some of these factors may be reduced to lower levels by heat treatment, such heat treatments are not always effective or desirable.
The present invention relates to the preparation of high protein content nutrient products from oilseed materials. Defatted oilseed material, such as soybean meal and related defatted soybean products, are particularly suitable for use in producing the modified high protein products of the present invention. As used herein, the term xe2x80x9cdefatted oilseed materialxe2x80x9d refers to oilseed material which has been processed to reduce the fat content by at least about 80%. The defatted oilseed material employed in the present process typically has a fat content of no more than about 5 wt. % and preferably no more than about 3.0 wt. % (dry basis).
Table 1 shows a comparison of an illustrative high protein/high FAN nutrient material produced from soybean meal according to the present process. The characteristics of a number of other nitrogen sources, unmodified soybean meal, soy protein concentrate (xe2x80x9cSPCxe2x80x9d), SoyTone(copyright) and a commercial yeast extract, are included in the Table for comparison purposes. The modified soybean meal (xe2x80x9cHigh-FAN Soyxe2x80x9d) has a protein content, FAN level and protein solubility comparable to that of SoyTone(copyright). The FAN level of the High-FAN Soy is considerably higher than that of SPC (which is comparable to unmodified soybean meal). The phytic acid content of the High-FAN Soy is negligible in contrast to that observed for SPC. The High-FAN Soy also has an extremely low level of soluble sugars similar to what is observed for SPC and yeast extract. In comparison, SoyTone(copyright) contains circa 4 wt. % stachyose. High-FAN Soy also has enhanced levels of vitamin B1 and B2 relative to unmodified soybean meal. It is notable that the High-FAN Soy is still a relatively crude unprocessed material (as reflected by the fiber content) in comparison to the highly processed commercial nitrogen sources.
The modified high protein products can be utilized in a wide variety of applications, including the preparation of fermentation media and the production of animal feeds, such as pet foods and related feeds for young animals. One embodiment of the invention provides a oilseed derived high protein material which has a FAN content of at least about 15 mg/g and very low levels of soluble sugars, such as raffinose, stachyose, saccharose.
The present invention also relates to a method for preparing the high protein nutrient from oilseed-based material. The protein content of the modified oilseed material produced by the present method is typically increased by at least about 5 to 10 wt. % relative to the initial unmodified material. Although less preferred, the same method may also be employed using an oilseed flake or meal completely retaining its natural oil constituents. The modified oilseed product is typically produced by a method which includes incubating a culture medium including the oilseed material until the medium has a protein content of at least about 55 wt. %. If the incubation step is carried out for a sufficient amount of time, the FAN content of the modified oilseed product can be quite high, e.g., at least about 15 mg/g and preferably about 20 mg/g or higher. The high protein modified oilseed products produced by the present method generally have low levels of soluble sugars (e.g., raffinose and stachyose) and, if desired, low levels of fat. The fiber content of the high protein modified oilseed products produced by the present method is generally quite similar to the fiber content of the original oilseed material prior to incubation.
In a preferred embodiment of the invention, the incubation of the culture medium is carried out for a sufficient amount of time to produce a high protein/high FAN version of the modified oilseed meal. The attributes of this product, at least about 55 wt. % and typically 60 wt. % or higher protein, FAN levels of 15 mg/g or above and low soluble sugar content make it an attractive material for use as a fermentation feedstock. The present process of modifying an oilseed product typically produces a material which contains substantially reduced levels of antinutritional factors (e.g., trypsin inhibitors) and antigenicity factors. The fiber content and amount of isoflavones in the modified oilseed material are generally relatively close to the corresponding levels present in the original unfermented oilseed material.
For some fermentation applications, it may be advantageous to produce a totally soluble protein source. This may be achieved by extracting soluble material from the biologically modified oilseed material into an aqueous solution. Such an extract typically has an even higher FAN and overall protein level than the crude modified oilseed product. The oilseed derived nutrient which is obtained through such an aqueous extraction is essentially completely soluble in water. As with the modified oilseed product, the extract is generally dried to a moisture content of no more than about 15 wt. % moisture and ground to form a granulated material, e.g., a powder in which at least about 95 wt. % of the particles have a particle size of no more than about 10 mesh. The dried extracts produced in this manner can have an overall protein content of 70 wt. % or higher and FAN contents of about 25 mg/g and above.